Calculate how a lump sum, plus optional monthly contributions, grows over time with compound interest, at any compounding frequency.
| Year | Contributed this year | Interest this year | Balance at year end |
|---|
Show calculation steps
How to use the compound interest calculator
- Enter your initial lump sum amount.
- Enter any monthly contribution you plan to add, or leave it at 0 for a one-time lump sum.
- Enter the expected annual interest rate and the number of years to project.
- Choose how often interest compounds, monthly, quarterly, annually, or daily.
- Click Calculate Growth to see the final value, total contributed, and total interest earned, with a year-by-year breakdown.
Why compounding frequency and time both matter
Compound interest grows faster than simple interest because each period's interest gets added to the balance and starts earning interest itself. Compounding more frequently, monthly instead of annually, adds a modest boost since interest gets credited and starts compounding sooner. But the biggest lever by far is time: money given more years to compound grows disproportionately more than the same amount invested for a shorter period, which is why starting early matters more than starting with a larger amount.
Example
An initial 100,000 with 5,000 added monthly, growing at 8% annual interest compounded annually over 15 years, grows to roughly 2,320,000, with total contributions of 1,000,000 and the rest coming from compound interest.
Frequently asked questions
- How is compound interest different from simple interest?
- Compound interest is calculated on principal plus previously earned interest, so growth accelerates over time.
- Does compounding frequency really make a noticeable difference?
- Yes, though the difference shrinks as frequency increases beyond monthly.
- Why do monthly contributions matter so much for long-term growth?
- Earlier contributions compound for longer, so starting early captures more of the compounding effect.
- Does this tool store or send my numbers anywhere?
- No, all calculations happen locally in your browser.
Bookmark this page and revisit it whenever your contribution amount or timeline changes, small early increases in monthly contributions compound into large differences over the long run.
0 Comments